Power supply circuits



Nov. 2, 1937. w. T. HUDTWALKER 2,097,882

POWER SUPPLY CIRCUITS Filed June 9, 1933 lNVENTOR MLL/AM 7'. #007[#41622 ATTORNEY from the voltage divider.

Patented Nov. 2, 1937 POWER SUPPLY CIRCUITS Wiliiam T. Hudtwalker,

Richmond Hill, N. Y.,

assignor to Radio Corporation of America, a corporation of DelawareApplication June 9, 1933, Serial No. 675,062

1 Claim.

The present invention relates to electrical networks and particularly tonetworks including thermionic tubes. V

In the usual method of energizing the electrodes of electronic tubesfrom the power supply mains of the normal alternating current network itis common practice to raise the voltage of the alternating current,rectify the resulting energy and then filter the rectified energy so asto remove the undesirable fluctuating component thereof. The usualset-up in such instances comprises a full wave rectifier the output ofwhich feeds into a filter circuit which is composed of choke coils andcondensers. The output of the filter circuit is then impressed across avoltage divider resistance element and the various desired voltages forthe energization of the thermionic tubes of a radio receiver or the likeare derived In the cases where the energization of thermionic tubesprovided with indirectly heated cathodes is contemplated it is common tosupply the rectifying and filtering system with current at the same timethat the heater element for the indirectly heated cathode of thethermionic tube is energized. In the tubes of thisnature, that is, tubesprovided with indirectly heated cathodes, a certain time period elapsesafter the heating circuit energy is supplied before the cathode assumesits normal action, that is, before the cathode is raised to a temperature which is sufiicient for electrons to boil off, so to speak.During this time period current obviously does not flow through thethermionic tubes with the result that the voltage built across thefilter condensers is greatly increased over the normal voltage andsometimes causes the condensers to break down. devised to, so to speak,delay the energization of the rectifier tubes until after the cathodesof the indirectly heated thermionic tubes assume normal operation.However. in such systems as are now known, various complications ariseand it is a fact that the expense of purpose is considerable.

It is an object of the present invention to provide an electricalnetwork whereby the harmful effects of the delay characteristics of atube provided with an indirectly heated cathode do not affect the filtersystem in any way harmful to the elements thereof. Another object of thepresent invention is to provide an electrical network that shallcompensate for the increase in voltage during the aforementioned timelag.

The foregoing objects thereto are attained in a and others ancillarypreferred embodiment Many systems have been delay circuits for this ofthe present invention by causing the output current of a rectifierfilter system to traverse an More specifically, is provided a currentnamed. conditions, that such characteristics that the potentialthereacross: is not the rate of change of current material that verysatisfactorily pose is commercially known as across the filter circuitthere path meeting the above is, a current path having rate of change oflinearly related to therethrough. A answers the pur- Thyrite and isdescribed in the United States Patent #1321742 to McEachron.

Thyrite, above, is a according to the patent referred to materialsomewhat similar to dry process porcelain throughout the mass of whichappear minute particles of conducting material.

The substance is substantially an insulator at low potentials andbecomes a continuously better conductor as the current through it isincreased.

For a better acteristics of the substance Thyrite understanding of thegeneral charreference is made to an article entitled Thyrite; A NewMaterial for Lightning Arrestors by K. B. Mc- Eachron, appearing inGeneral Electric Review, February 1930, page 92-.- From a reading of theabove mentioned article it may be gathered that Thyrite has acharacteristic.

The material Thyrite the form of discs each face hyperbolicresistance-ampere is usually utilized in of which is provided with asprayed metallic coating for contact purposes, however, it should beunderstood that the shape of the material is not a controlling factor.It should be noted, however, that the resistance of Thyrite variesdirectly with its thickness but The novel features that arecharacteristic of the present forth in particularity in the believed tobe invention are set appended claim.

will best be understood from the following description of a specificembodiment when read in connection with the accompanying drawing, the

single figure bodiment of of which represents a preferred emtheinvention showing the rectifier source of alternating current throughthe terminals I and 2 associated with the primary 4. A suitable switch 1is provided for turning the power on and off as desired in customaryfashion. One end of the secondary 5 is connected to the anode of arectifier tube 8 while the other end of the secondary 6 is connected tothe anode of rectifier tube 9. The cathodes of the rectifier tubes 8 andB have one side common as shown and are connected to a suitable sourceof energizing current not shown. The output of the rectifier tubes istaken as is usual in such cases from the center point of the secondary 6which is the negative side of the output and a point common to the twomentioned cathodes which is the positive side of the output inaccordance with the usual conventions.

The positive side of the rectifier output is connected to one end of avoltage divider resistance 12 through a pair of choke coils H! and Hwhile the negative side of the rectifier output is connected to theother end of thevoltage divider resistance 52. While choke coils l0 andH have been shown connected to the positive side of the rectifier outputit is to be distinctly understood that they may be just as wellconnected in the negative side of the rectifier output, and in fact, insome instances, connection in the negative side is desirable. The usualfilter condensers l3 and M are provided connected across the positiveand negative lines on either side of the choke coil H.

So far it is evident that the system described comprises the usualrectifier and filter circuit. A load adapted to be energized from theoutput of the filter circuit may comprise a tube of the screen grid typeand provided with an indirectly heated cathode. directly heated cathodeincludes the secondary 5 and a suitable resistance Hi. It should benoted that tube i5 is connected so that the potential on the cathode ishigher than the potential on the grid, hence, there is provided aso-called automatic bias for the grid in The anode of the tube isconnected to the top of the voltage divider resistance l2 although itmay "be connected to any point of resistance l2 de- The heater circuitfor the ill-' customary fashion.

readily energized immediately upon the closing of switch I it is obviousthat the load which comprises the tube I5 is, in reality, zero with theresult that a very much higher voltage exists across the condensers l3,I4 than the voltage existing across these condensers when the wholesystem is in normal operation. Accordingly, it has been found that thecondensers l3 and i4 must be built to withstand this added voltage withthe attendant increase in cost and size.

To overcome this drawback there are provided across the two condensersthe two Thyrite resistances l! and i8. While two of such resistanceshave been shown it is obvious that one may be sufficient for thepurpose. As connected, the two elements I! and i8 protect the filtercondensers l3 and 14 during the interval of time required by the tubessuch as IE to warm up and take a load. The two elements l1 and i8 willalso protect the network against surges and in addition they have afiltering effect when used in the position shown because the Thyriteelements present a lower impedance with increase of applied potentialthus tending to smooth out ripples.

The present invention is of particular importanoe in transmitterapparatus since in such cases the use of a device in which the load isnot taken immediately subjects associated equipment to voltage overload.

It is to be understood that the present invention is not limited to theuse of Thyrite or an equivalent material since many modifications willat once be apparent to those skilled in the art to which the inventionpertains, hence, the invention is not to be limited by the specificexemplifie cations shown for purposes of illustration but only by theprior art and by the spirit of the,

appended claim.

I claim:

A filter circuit for use in connection with power supply systemsutilized to energize thermionic tubes provided with indirectly heatedcathodes and wherein an appreciable period of time is required forenergizing the indirectly heated cathodes, said filter system includinga choke and at least one filter condenser, an additional filter meansshunted across the filter condenser comprising a device for protectingthe filter condenser during the period of time required to energize theindirectly heated cathodes, said device comprising an element composedof a granular material having a hyperbolic resistance-amperecharacteristic which is unaifected by variations in the rate of changeof voltage applied to the element to produce a flow of currenttherethrough, the resistance of said element being always substantiallythe same for a given density of current fiow through it whether thevalue of the said current density is attained by increasing or bydecreasing the current fiow, said additional filter means having adecreasing impedance with increasing applied potential across it wherebythe additional filter means operates to smooth out current passingthrough the filter circuit.

a WILLIAM T. HUDTWALKER.

